Unified multiple definitions of container_of() macro.

Removed duplicate definitions of the container_of() macro and
refactored sources to use the single implementation.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
diff --git a/src/text-backend.c b/src/text-backend.c
index 4ebbbdd..d33f703 100644
--- a/src/text-backend.c
+++ b/src/text-backend.c
@@ -35,6 +35,7 @@
 #include "compositor.h"
 #include "text-server-protocol.h"
 #include "input-method-server-protocol.h"
+#include "shared/helpers.h"
 
 struct text_input_manager;
 struct input_method;